1. Field of the Invention
This invention relates to a system for communication between semiconductor chips on a semiconductor substrate.
2. Description of the Prior Art
Prior art complex semiconductor circuits have often been constructed by use of plastic or ceramic circuit board having semiconductor packages mounted thereon with interconnection or communication between semiconductor packages taking place via conductors formed on the circuit board. Problems of heat dissipation and cross talk are minimized in such circuits by spreading out the components sufficiently on the circuit boards surface. It is also known in the prior art that, as the signal being communicated increases to a clock rate of over about 50 megahertz, the conductors on the printed circuit board begin to act as transmission lines and display capacitive and inductive properties. It is therefore necessary that appropriate measures be taken as in the case of transmission lines to obtain proper impedance matching to avoid reflections and the like. This problem is relatively minor and, in general, no particular attention was needed in the past if the check rate was below about 10 megahertz. However, with the continued emphasis in high speed operation of the components and with the increased miniaturization of the integrated circuit chips themselves and the desire for higher packing density on the printed circuit boards, the above noted problems become more and more of a bottleneck. For example, the number of pins entering and exiting integrated circuit packages is continually increasing due to the rapidly increasing number of components contained therein. This materially increases the problem of matching each pin and the path thereto or therefrom from reflections and other transmission line type problems. Furthermore, substantial heat will be generated in the input and output drivers, both from the increase in component packing density per chip as well as the increase in packing density of the chips on the printed circuit board.